CARBON IN BETA-RHOMBOHEDRAL BORON

Carbon atoms in the beta-rhombohedral boron structure substitute for b oron atoms at the polar sites of the B-12 icosahedra. The donor level of the excess electron of carbon coincides with the upper valence band , thus raising the hopping probability within this band. This assumpti on is consistent with various experimental results. The ionisation ene rgy of the intrinsic electron trapping levels is slightly different fo r B-12 and B11C icosahedra. The photoconductivity and quotient spectra of the reflectivities of differently doped samples indicate carbon-in duced changes in the density of states within the energy bands.